Could vitamin A levels affect tuberculosis risk?

Researchers from Harvard Medical School (MA, USA) have discovered that individuals with low levels of vitamin A may be up to 10-times more likely to develop tuberculosis (TB) when exposed to infected individuals. This suggests vitamin A supplementation could be a potential tool to help prevent the spread of TB.

It has previously been reported that vitamin A might play a role in modulating the immune system and the course of infection; however, with regards to TB this has remained an unknown. In this study, published recently in Clinical Infectious Diseases, the team hoped to determine host factors involved in modulating the risk of TB infection.

The researchers assessed TB patients who sought treatment at 106 clinics around Lima, Peru, reaching out to their household contacts. In total, 6000 household contacts enrolled in the study, each giving an initial blood sample before undergoing regular follow-up for approximately a year.

Of the 6000 participants, 258 developed TB. The team compared the blood samples of 180 of these individuals with randomly-selected control samples from those that did not develop TB, matching on gender and age. The researchers discovered a 10-fold increase in the risk of developing TB in participants with vitamin A deficiency (defined as less than 200 micrograms per liter of blood).

The protective effect appeared to dose-dependent, becoming stronger with increasing levels of vitamin A, well above what is considered minimum healthy level. In addition to this, the researchers demonstrated that the risk was higher in younger individuals, specifically those aged 10–19.

The team reported that the correlation between vitamin A and risk of TB infection was strong even after adjustment for confounding factors including socioeconomic status and nutritional factors.

Senior author Megan Murray (Harvard Medical School) commented: “This is one of the strongest risk factors reported in a large epidemiological study in years. If the link is affirmed in a clinical trial of vitamin A supplementation, it would make a powerful case for using this approach to prevent TB in people at high risk of disease.”

TB disproportionately affects low- and middle-income countries where vitamin A deficiency can affect up to 30% of the population. This statistic, along with the findings from this study, suggest that vitamin A supplementation may be able to prevent the spread of TB, however, the team warn that further research, including a clinical trial, would be required to confirm these results.

Murray concluded: “It’s exciting to think that something as simple and inexpensive as supplementing people’s diets with vitamin A may be a powerful tool for preventing TB.”

“TB is a tough disease to live with, and a tough disease to treat. We’d love to keep people from getting sick in the first place.”